Truck pivot joint bearing and method of lubricating

ABSTRACT

A bearing assembly is disclosed having a pair of bearing members movable relative to one another. A space is defined between the bearing members, and a relatively thin coating of a greaseless, self-lubricating material is applied to the surface of at least one of the bearing members. A grease lubricant is disposed in the space defined between the bearing members such that both the grease lubricant and the greaseless material act to substantially lower the friction-generated heat that is encountered during operation.

FIELD OF THE INVENTION

The present invention relates to bearing assemblies, and moreparticularly to bearing assemblies having two bearing members movablerelative to one another and methods of lubricating these assemblies.

BACKGROUND OF THE INVENTION

Various bearing assemblies and methods of lubricating these assembliescan be found in many applications. Typical bearing assemblies include apair of bearing members that are movable relative to one another. Morespecifically, a bearing or bushing is typically a cylindrical shell,with or without a flange, installed in a structural housing inconjunction with a mating shaft, pin, or bolt. Bearings having pinnedjoints typically are used for cyclic and oscillatory motion, such asused in landing gear joints, control surface hinge points, and actuatinglinkages.

The advantages of bearings are numerous. Bearings are relativelyeconomical replacement elements which extend the useful life of majorstructural elements by providing protection from wear, corrosion,deformation, and other service-limiting or failure-initiating damage.The two basic considerations for successful service performance of abearing are strength and life. Strength is the capability of the bearingto resist deformation and structural failure under static load. The lifeof the bearing is determined by its ability to resist wear, fretting,galling, and seizure under cyclic or oscillating motion.

FIG. 1A shows a typical bearing structure assembly 100, wherein grease106, such as Royal MS 11 manufactured by Royal Lubricants, Inc. of EastHanover, N.J., is applied between bearing assembly members comprising abearing 101 and pin 103 to lubricate the members as they move relativeto one another. Specifically, the grease 106 is disposed between theinner surface 102 of the bearing 101 and the outer surface 104 of thepin 103. While grease is suitable for many applications, extremepressure and movement by the bearing assembly members may cause thegrease to lose its lubricity, which may lead to overheating and eventualfailure of the bearing assembly and surrounding structures.

One application where this may occur is on a landing gear apparatus ofan aircraft, and more particularly on a truck pivot joint bearingassemblies for an aircraft landing gear. The bearing assemblies used inthis type of application typically include a relatively thick coating ofgrease between the moving surfaces of the bearing. This is acceptablefor most circumstances because the dynamic bearing pressures and slidingvelocities of the moving surfaces are relatively low. However, roughlanding conditions, such as runways with deep cracks, crevices,potholes, and/or uneven surfaces, can cause excessive use of and wear onthe truck pivot joint bearing assemblies from the rapid shocks andextreme oscillations these surface abnormalities transfer to the bearingassemblies. In some cases, it has been discovered that these roughconditions create as much as ten (10) times more energy than isgenerated under normal conditions. This additional energy is absorbed asheat by the bearing assemblies, which accounts for the damage thatoccurs when using conventional bearing assemblies in these environments.As a result, the high temperatures generated in these conditions causethe grease packed between the moving surfaces of the bearing assembliesto melt away and thus lose its effective lubricity. This is shown inFIG. 1B, wherein the grease 106 is no longer occupying the entire spacebetween the opposing bearing members 101, 103, which allows the innersurface 102 of the bearing 101 to have intimate contact with the outersurface 104 of the pin 103.

As the grease loses lubricity and the surfaces 102, 104 of the bearingassembly 100 begin to directly move against each other, severe damage orfailure of the bearing assembly components is likely. To prevent failureof the bearing assembly, time-consuming maintenance must be performedmore frequently, which further adds to the cost of maintaining theaircraft in addition to the lost profits while the aircraft is undermaintenance or repairs. Thus, it is desirable to provide a lubricant tobearing components that is more resistant to dynamic bearing pressuresand heat generation in extreme conditions.

FIG. 2A shows another type of conventional bearing assembly. Inparticular, the bearing assembly 110 includes a bearing 111 and a pin113 having opposing surfaces 112 and 114, respectively. A dry,greaseless coating material 116 is applied to a desired surface byspraying or coating the surface, such as the inner surface 114 of thebearing 111. The greaseless, self-lubricating material 116 occupies thespace between the opposing bearing surface 112, 114 such that thesurfaces are only separated by the greaseless material. One example of agreaseless self-lubricating material 116 is a polyester, thermosetting,resin-based material incorporating polytetrafluoroethylene or TEFLON®particles, such as the material manufactured under the name KARON byKamatics Corporation of Bloomfield, Conn. This type of material isproclaimed as self-lubricating, meaning no external grease is requiredto lubricate the bearing assembly 110. Indeed, greaseless lubricantssuch as shown in FIG. 2 were designed to overcome the disadvantages ofgrease lubricants shown in FIG. 1, particularly in terms of loadcapacity and service life. Other types of greaseless lubricants aredescribed in U.S. Pat. Nos. 3,929,396 and 3,996,143.

In particular, greaseless, self-lubricating materials operate at lowerfriction levels, which reduces the heat generated during operation. Ifheat does build up, the polytetrafluoroethylene particles typicallyexpand more rapidly than the underlying surfaces to fill the spacebetween the bearing surfaces, so that frictional contact between bearingsurfaces 112, 114 is thwarted or delayed, at least temporarily.Conventional practice teaches that a thicker coating of the greaselessmaterial 116 will provide more lubrication for the bearing 110. Whiletrue for most applications, the extreme loading conditions mentionedabove may cause the greaseless material to break down. And because thegreaseless material 116 allows the bearing surfaces 112, 114 to beessentially in contact with each other separated only by the greaselesslubricant, any reduction in the thickness of the greaseless lubricantcan reopen the space between the bearing surfaces, which can damage thebearing or cause the bearing to fail. This is shown in FIG. 2B, whereinthe greaseless material 116 has worn down in certain areas, which allowsunwanted and damaging rattling or movement between the bearing assemblymembers 111, 113. Thus, while greaseless lubricants provide advantageousqualities over grease lubricants, there is a need to provide a bearingassembly having a lubricant that offers even better wear and heatresistance, which leads to longer operational life of the bearing. Thereis also a need to provide a bearing assembly having a lubricant that isresistant to extreme loading conditions, such that the lubricantprovides longer protection to the bearing in these environments comparedto protection from conventional lubricants before service is required.

SUMMARY OF THE INVENTION

These and other needs are provided, according to the present invention,by a bearing assembly that combines the benefits of greaseless lubricantmaterials and traditional grease lubricants to provide longer bearinglubrication and protection compared to conventional bearings and methodsof lubricating the bearings. The bearing assembly of the presentinvention has been shown to provide up to 600% longer life thanconventional grease-lubricated bearings under certain operatingconditions, which greatly reduces the maintenance cost and frequency ofthe bearing.

In particular, the bearing assembly of the present invention comprises apair of bearing members that are movable relative to one another. Themembers are typically metal, although other materials may also be used.In one embodiment, at least one of the members is formed of an aluminum,nickel, and bronze alloy, which is preferable because it has shown to bevery durable and highly resistant to wear. In addition, the members arespaced a slight distance apart to define a space therebetween, such asbetween 0.006-0.008 inch. At least one of the bearing members has abearing surface having a relatively thin coating of a self-lubricating,greaseless, polytetrafluoroethylene-based material thereupon. Thecoating, which according to one embodiment is about 0.003-0.007 inch,can be applied one of many ways, including spraying, coating, ordipping.

The thin coating of greaseless material does not occupy the entire spacebetween the pair of bearing members. The remaining space is insteadoccupied by a grease lubricant. Accordingly, the grease lubricant andthe greaseless lubricant act in conjunction with one another tolubricate the bearing members. Advantageously, it has been discoveredthat, despite the teachings that greaseless lubricant materials are notto be used in conjunction with grease lubricants, a dramatic improvementin bearing and lubrication life is realized by combining a relativelythin layer or coating of greaseless lubricant with a grease lubricant inthe space defined by the bearing members.

The bearing assembly of the present invention is particularlyadvantageous for use in extreme conditions, such as where the bearingassembly is subjected to great dynamic pressures and oscillations. Forexample, truck pivot joint bearing assemblies used in aircraft landinggear are prime candidates for employing the teachings of the bearingassembly of the present invention, as truck pivot joint bearingassemblies may encounter great dynamic pressures and oscillations duringlanding cycles. Of course, the bearing assembly of the present inventioncan also be used in many other applications where the loading conditionsare not extreme, as the longer lubrication and bearing life isappreciable in a broad range of applications.

Thus, the present invention provides a bearing assembly having animproved bearing life and requiring less frequent maintenance cycles tothe bearing components. By combining the thin layer of greaselessmaterial with a grease lubricant in the space defined between the twobearing members, at least two advantages are realized. First, the thinlayer or coating of greaseless material provides a lower coefficient offriction compared to grease lubricants, which delays the onset of heatbuildup and loss of lubricity. Second, the grease lubricant provides aless-rigid material for moving about and occupying the space between thebearing members, which further improves bearing life.

By contrast, using only a greaseless coating (i.e., a relatively thickcoating as taught by conventional bearings) between the bearing memberscan result in unwanted play between the surfaces of the bearing assemblyas the coating wears away. By using a relatively thin greaseless coatingin conjunction with a grease lubricant, the greaseless lubricantreceives little or no contact with the opposing bearing surface and thuswears more slowly. In addition, the grease lubricant fills the spacebetween the bearing assembly surfaces to prevent unwanted movement orplay. And because the thin greaseless coating reduces the friction andheat generated during loading cycles, the grease lubricant's life spanis increased. Thus, the bearing assembly of the present inventionprovides a clear advantage over conventional bearing assemblies andlubrication techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIGS. 1A and 1B are cross-sectional views of a bearing assemblyaccording to the prior art;

FIGS. 2A and 2B are cross-sectional views of a bearing assemblyaccording to the prior art;

FIG. 3 is a side view of a landing gear assembly for an aircraftaccording to one embodiment of the present invention;

FIG. 4 is a cross-sectional view of a truck pivot joint bearing of thelanding gear assembly as viewed along line 4-4 of FIG. 3;

FIG. 5 is a side perspective view of a truck pivot bushing according toone embodiment of the present invention;

FIG. 6 is a cross-sectional view of a truck assembly according to oneembodiment of the present invention; and

FIG. 7 is a cross-sectional view of a bearing assembly as viewed alongline 7-7 of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

FIGS. 3-6 show various views of portions of a landing gear assembly 10for an aircraft, such as a Boeing 757. The landing gear assembly 10includes at least one shock strut 12 that is rotatably connected to atruck pivot pin 24. Specifically, the shock strut 12 defines an openingfor rotatably receiving the truck pivot pin 24. The shock strut 12 alsoincludes a distal portion called an inner cylinder fork 26 that extendsaway from the opening. The landing gear assembly 10 also includes atruck pivot bearing assembly, shown generally as 20. The bearingassembly 20 includes a truck assembly 14 that is rotatably connected tothe truck pivot pin 24, and at least two pairs of wheels 16 are attachedto the truck assembly 14.

FIGS. 4 and 6 show cross sectional views of the bearing 20, wherein FIG.6 is a cross sectional view of the truck assembly 14 forming part of thebearing 20 shown in FIG. 4. As shown in FIG. 6, the truck assembly 14defines a cavity 34 therethrough having an inner surface 31. The truckassembly 14 is preferably formed of metal, such as a high strength steelalloy, although other metals or materials may also be used, such astitanium. The truck pivot pin 24, which in one embodiment is a chromeplated pin, extends through the cavity 34 of the truck assembly 14. Apair of truck pivot bushings 30 are positioned at opposing ends of thetruck assembly 14 such that flanged surfaces 33 of the pivot bushingsengage sidewalls 23 of the truck assembly. In addition, a pair ofback-to-back inner cylinder pivot bushings 40 are positioned proximatethe inner cylinder forks 26 such that the inner cylinder assemblies areseparated from the truck assembly 14 by the pivot bushing 30 and theinner cylinder pivot bushings 40. In this regard, the truck pivotbushings 30 and inner cylinder pivot bushings 40 provide low-frictionsupport to the truck pivot pin 24 as it rotates inside the truckassembly 14 and shock struts 12. A splined washer 28 helps secure theinner cylinder pivot bushings 40 about the pivot pin 24, and multiplepairs of brake rods 42 extend substantially parallel to the truckassembly 14.

As shown in FIG. 4, the pivot bushings 30 are interposed between thetruck assembly 14 and the truck pivot pin 24. As shown in FIG. 5, eachpivot bushing 30 is generally tubular, and preferably defines aplurality of lubrication distribution grooves 36 that receive anddistribute grease between the truck pivot pin 24 and the pivot bushings30 so that the pivot pin 24 is rotatable relative to the truck assembly14. Each pivot bushing 30 also includes an outer surface 32 that ispositioned proximate the inner surface 31 of the truck assembly 14 in apress-fit or interference fit so that the pivot bushing 30 does not moverelative to the truck assembly 14. A seal 38 is disposed proximate thelubrication distribution grooves 36 such that grease or other lubricantis prevented from escaping. According to one embodiment, the seal 38 isformed from an elastomer, although other materials could also be used toform the seal. As shown, each pivot bushing 30 engages a sidewall 23 ofthe truck assembly 14 and an adjacent inner cylinder pivot bushing 40 tofurther seal the pivot bushing and the truck assembly 14.

FIG. 7 shows a detailed cross-sectional view of the truck assembly 14,pivot bushing 30, and pivot pin 24 according to a preferred embodimentof the present invention. In particular, the pivot bushing 30 isdisposed radially inwardly of the truck assembly 14 and is securedthereto by a frictional interference fit. The inner surface 35 of thepivot bushing 30 is proximate the pivot pin 24, and an advantageouslubricant according to the present invention is interposed therebetween.According to one embodiment, the inner surface 35 of the pivot bushing30 is coated with a greaseless, self-lubricating material 50. It is alsopossible to apply the relatively thin coating of greaseless material 50on both the inner surface 35 of the pivot bushing 30 and the outersurface of the pivot pin 24. Alternatively, only the outer surface ofthe pivot pin 24 may be coated with the greaseless material 50, althoughpreferably only the inner surface 35 of the pivot bushing 30 includesthe greaseless material 50. The material 50 is preferably apolytetrafluoroethylene-based material, such as a material sold underthe trade name KARON by Kamatics Corporation of Bloomfield, Conn. Thegreaseless material 50 can be applied to the inner surface 35 of thepivot bushing 30 in a number of ways, such as spraying, brushing on, orby dipping the pivot bushing 30 in a bath of the greaseless material.The greaseless material 50 includes a solid particulate, such aspolytetrafluoroethylene or TEFLON®, that is embedded in a stabilizermaterial in the form of flocked, powdered, fibrous, flaked, beaded, orother forms. Other particulate materials may also be used, such assilver powder, lead powder, and the like. The greaseless material 50 hasa thickness of about 0.003-0.007 inch, and preferably about 0.005 inch.As shown in FIG. 7, the thickness of the greaseless material 50 is notenough to substantially fill the space defined by the pivot bushing 30and the pivot pin 24.

Advantageously, the space defined by the pivot bushing 30 and the pivotpin 24 not occupied by the greaseless material 50 is occupied or filledby a grease lubricant 58, such as an extreme pressure grease sold underthe name ROYCO 11MS manufactured by Royal Lubricants, Inc. of EastHanover, N.J. Other types of greases may also be used, such as anyextreme pressure grease that is apparent to one of skill in the art. Thechosen grease must be highly resistant to extreme dynamic bearingpressures and temperatures.

The combination of a relatively thin coating of the greaseless material50 coupled with the grease lubricant 58 as disclosed by the presentinvention flies in the face of conventional lubrication systems andmethods. In this regard, it has been discovered that applying arelatively thin coating, such as about 0.005 inch, of the greaselessmaterial 50 in combination with the grease lubricant that fills theremainder of the gap between the pivot bushing 30 and the pivot pin 24allows dynamic bearing pressures to be increased dramatically to a levelthat approaches the allowable pressures for the base bearing material.More particularly, the relatively thin layer or coating of greaselessmaterial 50 has a friction coefficient of only about 0.08, whereasgrease lubricants have a friction coefficient of about 0.20. Asdiscussed above, conventional applications of greaseless materialcoatings call for much thicker coatings, which has been discovered tolimit their use at relatively low dynamic bearing pressures and slidingvelocities. Accordingly, the bearing assembly 20 according to thepresent invention can operate longer under extreme conditions, such aswhen landing aircraft on very rough runways where the bearing receivessevere oscillations and sliding velocities. Specifically, the bearingassembly 20 according to the present invention reduces thefriction-generated heat sufficiently to substantially reduce oreliminate damage to the truck assembly 14 or inner cylinder assembly 26.

Another advantage of the bearing assembly 20 according to the presentinvention is that the combination of greaseless, self-lubricatingmaterial 50 and the grease lubricant 58 can be applied in existingbearing assemblies, such as those found in aircraft landing gearassemblies, without having to redesign the assemblies to handle theextreme conditions. Thus, existing aircraft landing gear can easily beretrofitted with the bearing assembly 20 of the present invention, whichis significantly less expensive than redesigning a new type of landinggear assembly or bearing configuration. In addition, the bearingassembly 20 of the present invention requires less frequent maintenancecompared to conventional bearings operating under similar conditions,which substantially reduces maintenance man hours, downtime, and overalloperating costs. In fact, it has been discovered that up to a 600%improvement in life span is achieved in comparison to conventionalgrease-lubricated bearings by applying the bearing assembly 20 of thepresent invention to truck pivot joint bearings in large jet aircraftlanding gear assemblies.

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed andthat modifications and other embodiments are intended to be includedwithin the scope of the appended claims. For example, the teachings ofthe present invention, namely a bearing assembly 20 having therelatively thin coating 50 of greaseless, self-lubricating material incombination with a grease lubricant 58 used in combination in the spacedefined between the inner and outer members of a bearing assembly, canbe applied to many industries in addition to the aerospace industrywhere lower friction bearings are desired. In addition, the teachings ofthe present invention regarding the combination of a greaseless,self-lubricating material used in combination with a grease lubricantcould be applied to a broad range of applications, including applyingthe combination to a nut and bolt combination, or similar applications.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

1. A bearing assembly, comprising: a pair of bearing members movablerelative to one another, said pair including a first member and a secondmember that define a space therebetween, at least said first memberhaving a bearing surface having a coating of a thermosettingpolytetrafluoroethylene-based resin material thereupon with a thicknessof about 0.003-0.007 inch, the polytetrafluoroethylene-based resinmaterial of the coating including solid particulates embedded in astabilizer material, the coating of the polytetrafluoroethylene-basedresin material extending continuously along the bearing surface of saidfirst member; and a grease lubricant occupying the space defined betweenthe first member and the second member but separated from the bearingsurface of the first member by the coating of thepolytetrafluoroethylene-based resin material, wherein thepolytetrafluoroethylene-based material and the grease lubricant act inconjunction with one another to lubricate the first and second members.2. A bearing assembly according to claim 1, wherein the solidparticulate is in a form selected from at least one of the groupconsisting of flocked, powdered, fibrous, flaked, and beaded.
 3. Abearing assembly according to claim 1, wherein the first member isformed from at least one of the group consisting of steel, titanium,aluminum, nickel, and bronze.
 4. A bearing assembly according to claim1, further comprising a seal positioned in the space defined between thefirst member and the second member.
 5. A bearing assembly according toclaim 1, wherein the coating is a self-lubricating material.
 6. Abearing assembly according to claim 1, wherein bearing surfaces of thefirst and second members are spaced apart by a distance between 0.006inch and 0.008 inch.
 7. A bearing assembly for a truck pivot jointbearing in an aircraft landing gear, the assembly comprising: a metallictruck assembly defining an opening therein; a pin rotatably positionedin the opening of the truck assembly; a truck pivot bushing positionedat least partially in the opening defined by the truck assembly, thetruck pivot bushing having an inner surface proximate said pin such thata space is defined between the inner surface of the truck pivot bushingand the pin, at least the inner surface of the truck pivot bushinghaving a coating of a thermosetting, self-lubricating, greaselesspolyester resin material with a thickness of about 0.003-0.007 inch, thecoating including solid particulates embedded in a stabilizer material,the coating extending continuously along the inner surface of the truckpivot bushing; and a grease lubricant occupying the space definedbetween the pivot bushing and the pin but separated from the innersurface of the truck pivot bushing by the coating.
 8. A bearing assemblyaccording to claim 7, wherein the coating is apolytetrafluoroethylene-based material.
 9. A bearing assembly accordingto claim 8, wherein the solid particulate is in a form selected from atleast one of the group consisting of flocked, powdered, fibrous, flaked,and beaded.
 10. A bearing assembly according to claim 7, wherein thepivot bushing is formed from at least one of the group consisting ofsteel, titanium, aluminum, nickel, and bronze.
 11. A bearing assemblyaccording to claim 7, further comprising a seal positioned in the spacedefined between the truck assembly and the pin.
 12. A bearing assemblyaccording to claim 7, wherein the inner surface of the truck pivotbushing and the pin are spaced apart by a distance between 0.006 inchand 0.008 inch.
 13. A bearing assembly, comprising: a pair of bearingmembers movable relative to one another, said pair including a firstmember and a second member that define a space therebetween, said firstmember having a bearing surface having a coating of a thermosettingpolytetrafluoroethylene-based resin material thereupon that occupiesless than the space defined between the first member and the secondmember, the coating having a thickness of about 0.003-0.007 inch, thecoating including solid particulates embedded in a stabilizer material,the coating of the polytetrafluoroethylene-based resin materialextending continuously along the bearing surface of the first member;and a grease lubricant occupying a remaining space defined between thecoating of the first member and the second member but separated from thebearing surface of the first member by the coating of thepolytetrafluoroethylene-based resin material, wherein thepolytetrafluoroethylene-based material and the grease lubricant act inconjunction with one another to lubricate the first and second members.14. A bearing assembly according to claim 13, wherein bearing surfacesof the first and second members are spaced apart by a distance between0.006 inch and 0.008 inch.
 15. A bearing assembly for a truck pivotjoint bearing in an aircraft landing gear, the assembly comprising: ametallic truck assembly defining an opening therein; a pin rotatablypositioned in the opening of the truck assembly; a truck pivot bushingpositioned at least partially in the opening defined by the truckassembly, the truck pivot bushing having an inner surface proximate saidpin such that a space is defined between the inner surface of the truckpivot bushing and the pin, at least a portion of the inner surface ofthe truck pivot bushing having a coating of a thermo setting,self-lubricating, greaseless polyester resin material that occupies lessthan the space defined between the inner surface of the truck pivotbushing and the pin, the coating having a thickness of about 0.003-0.007inch, the coating including solid particulates embedded in a stabilizermaterial; and a grease lubricant occupying a remaining space definedbetween the coating of the inner surface of the truck pivot bushing andthe pin but separated from the inner surface of the truck pivot bushingby the coating.
 16. A bearing assembly according to claim 15, whereinthe inner surface of the truck pivot bushing and the pin are spacedapart by a distance between 0.006 inch and 0.008 inch.